Genetic identification of neurons controlling a sexually dimorphic behaviour

In the fruit fly Drosophila melanogaster, locomotor activity is sexually di morphic: female flies constantly modulate their activity pattern whereas ma les show a steadier, stereotyped walking pace [1]. Here, we mapped the area of the brain controlling this behavioural dimorphism. Adult male Drosophil a expressing a dominant feminising transgene in a small cluster of neurons in the pars intercerebralis exhibited a female-like pattern of locomotor ac tivity. Genetic ablation of these neurons prevented the feminisation of the locomotor activity of transgenic males, The results suggest that this clus ter of neurons modulates sex-specific activity, but is not involved in init iating fly locomotion, Nor does it control male courtship behaviour, becaus e feminisation of courtship was not correlated with the feminisation of loc omotor activity.